Damaged or diseased bones and joints in human and animal patients give rise to pain and decreased joint mobility. It is known to totally or partially replace these bones and joints with artificial implants to alleviate the painful symptoms and restore some degree of mobility.
The replacement of bones in the wrist has had limited success because of the complexity and multitude of bones, tendons and ligaments in the wrist. As can be seen in FIG. 1, there is a first row of wrist bones, known as a first carpal row or proximal carpal row, adjacent a radius bone and an ulnar bone. The proximal carpal row includes a scaphoid bone, a lunate bone, a triquetrum bone and a pisiform bone. A second row of bones, known as a distal carpal row, includes a trapezium bone, a trapezoid bone, a capitate bone and a hamate bone. The scaphoid bone is surrounded by the trapezium, trapezoid, capitate and lunate bones and articulates at the proximal side with a radius bone of the arm, at the distal side with the trapezium and trapezoid of the proximal carpal row, and medially about the lunate and capitate bones. The distal end of the radius bone has a scaphoid fossa, which faces the scaphoid, and a lunate fossa which faces the lunate bone. A ridge separates the scaphoid and the lunate fossas.
The ligaments of the wrist are illustrated in FIGS. 2A and 2B for two different patients demonstrating the complexity of the wrist anatomy and the variability of the wrist anatomy between different patients. These ligaments include the radial collateral ligament (RC), the radioscaphocapitate ligament (RSC), the radiolunate ligament (RL), the ulnolunate ligament (UL), the ulnocarpal meniscus homologue (M), the lunotriquetral ligament (LT), the deltoid ligament (V), dorsal scapholunate ligament (SL), dorsal interior circular muscle unit (DIC), ulnar collateral (UC), radioscapholunate ligament (RSL), trapezoid-trapezium (TT), trapezoid-capitate (TC), capitohamate (CH), radioscaphoid (RS), radiotriquetral (RT). The Volar FCR tendon and the volar capsule also form part of the wrist anatomy but are not shown in FIGS. 2A and 2B.
Replacement of some of the bones of the wrist may be required to treat bone fractures, or diseases such as arthritis which affects the radius joint of the wrist. Arthritis more commonly affects elderly patients and results in painful joints, and may be so severe that the pain cannot be managed with pain medication and the arthritic hand cannot be used to lift weight. Wrist bone fractures, seen typically in younger patients, occur most often in the scaphoid bone. Damage or degeneration to the scaphoid bone can also occur through conditions other than fracture. The scaphoid bone is particularly difficult to heal since blood supply to the scaphoid bone is provided only by vessels on the distal side. If not treated properly or detected early, a scaphoid bone fracture can lead to bone necrosis.
Total or partial wrist replacements are known to treat arthritis in the wrist and involve the replacement of several bones in the wrist using a total wrist replacement prosthesis formed from biomaterials such as metal, polypropylene or silicone elastomers. In one known total wrist replacement system, the bones of the first carpal row are removed and replaced by an implant which fuses together the bones above the first carpal row and which has an articulating surface for articulating against the radius or a surface implant replacing the surface of the radius. With this type of replacement, the pain may be somewhat alleviated although patients cannot retain full functional flexibility and use of their hand. These types of replacements can also loosen through trauma or injury sustained through a fall, for example, or through wear, and therefore require replacement. Partial wrist replacements are a less severe type of replacement. A known partial wrist replacement technique involves the replacement of the scaphoid and lunate bones of the proximal carpal row with an implant which functions as a spacer to maintain the relationship of adjacent carpal bones after excision of the scaphate or lunar bones.
The known early treatment for scaphoid bone fracture is anatomic reduction with internal fixation. Known fixation devices include Herbert's screw, the Acutrack Acumed™ screw, as well as other screw types. Typically, the fractured scaphoid bone and/or its fragments are removed and some of the remaining bones are fixed to one another using one or more screws. Clearly, this can restrict the range of movement of the patient's wrist and is not ideal. Late treatment involves the treatment of resultant arthritis with a partial or total wrist replacement. Ligament injury between the scaphoid and lunate is often missed and the most common treatment is partial or total wrist replacement.
The bones of the human or animal foot can suffer from similar damage or diseases as the wrist. As for the wrist, there is a lack of effective treatment for damaged or diseased foot bones and ligaments.
Therefore, it is desired to overcome or reduce at least some of the above-described problems.